To identify the problematic CICs, you have to check the average conversation time on each CIC. it should be very less for the problematic CICs. (whenever the call is routed through a problematic CIC, the user tend to disconnect it after few seconds thus making the conversation time shorter). you can also request your NSS team to carry out a no-audio or audio loop back testing for all the CICs of the respective BSC.
To identify the problem at the radio side, i think you should conduct a walk test of drive test (whatever suits you), see the quality situation, also focus on RLINK TIMEOUT COUNTER when the call drops. may be you can make out something out of it